The present invention concerns a device for moving a welding torch during the welding of seams, especially of circumferential seams, with a chassis, which is equipped with a feed motor and with a feed motor control unit.
Reference is made to the state of the art, as it has been known, e.g., through the West German Offenlegungsschrift No. 22 43 460. The device, according to this West German Offenlegungsschrift, has a feed motor, with which the chassis and thus also the welding torch can be moved orbitally around a pipe being welded. Practice has shown that the constancy of the feed/rotation speed that can be achieved with devices of this type is in the order of magnitude at which perfectly welded seams are not always guaranteed. These changes in the feed speed are attributed especially to the variable effects of the forces due to inertia during the movement of the chassis around a pipe being welded.
It has also been found that both in the above-described orbital chassis and in the longitudinally moving chassis, in which the feed motor is connected with the drive wheels of the chassis via transmission and gears, the play of the transmission has an effect on the constancy of the travelling speed. This effect is especially intensive during the reversal from forward motion to return motion in the case of longitudinally moving chassis, in which case velocity lags occur. Velocity jumps occur in the case of orbital chassis at the transition ascent to descent and vice versa; these also have an adverse effect on the welding process as well as on the quality of the welding.